1. Field of the Invention
This invention relates to an electrode for level detection used for detecting level of a liquid or a powder.
2. Description of the Prior Art
A conventional electrode for level detection is of a structure comprising a lead electrode formed on the upper surface of an insulating substrate or base plate, and a detection electrode formed in a stripe shape from the lead electrode to the lower end portion of the substrate.
When the electrode of the above structure which is referred to as a first electrode and another electrode of the same structure as the first electrode which is referred to as a second electrode are oppositely disposed in a fluid to be measured (e.g., a battery electrolyte or a conductive toner) to measure impedance between the first and second electrodes, impedance changes in dependency upon the length of the portion of the detection electrode which is not immersed by the fluid to be measured. Thus, the level of the fluid can be detected.
For example, when a resistor is used as the detection electrode, where the fluid to be measured has a conductive or resistive property, level detection can be made by the resistance value between the first and second electrodes.
Further, when a conductor is used as the detection electrode, where the fluid to be measured has a resistive property, level detection can be made by the resistance value between the first and second electrodes, and where the fluid to be measured has a dielectric property, level detection can be made by the electrostatic capacitance value between the first and second electrodes.
In addition, when a dielectric resin coated conductor is used as the detection electrode, even in the case where the fluid to be measured has a conductive property or a dielectric property, level detection can be made by the electrostatic capacitance value between the first and second electrodes.
In the case of an electrode for level detection using a resistor as the detection electrode, there is unevenness in the characteristic resulting from unevenness in the production.
Since the electrode for level detection is relatively frequently exchanged because of corrosion, reproducibility of the characteristic is required. Thus, trimming is carried out to make an adjustment so that unevenness as stated above does not result.
However, since the detection electrode is a continuous elongated member in the conventional electrode for level detection, there is difficulty in trimming. Accordingly, there is a limitation in adjustment, resulting in poor reproducibility or yield.
Further, there are instances generally in the conventional electrode for level detection where the height of the portion of the detection electrode with which the fluid to be measured is in contact and the height of the portion of the detection electrode with which another fluid to be measured is in contact may differ from each other because the surface tensions of the both fluids are different from another one. As the result, errors in measurement do not fall within a fixed range, leading to the problem that valuation of accuracy or assurance of accuracy becomes difficult.
In addition, when the drop of a fluid to be measured adheres to the surface of a detection electrode under the state where that drop is contiguous to the fluid to be measured, there is also the problem that an error corresponding with the volume of the drop might occur.
In view of this, a technique to prevent adhesion of a drop of fluid by application of ultrasonic vibration has been proposed. However, even with this technique, a new problem that the device becomes complicated might occur.